Internet of Things (IoT) radio networks are becoming popular in several scenarios for short-range applications (e.g., wearables and home security) and medium-range applications (e.g., shipping container tracking and autonomous farming). They have also been proposed for water monitoring in flood warning systems. IoT communications may use long range (LoRa) radios working in the 915 MHz industrial, scientific and medical (ISM) band. In this research, we study the propagation characteristics of LoRa chirp radio signals close to and over water in a tropical meadow region. We use as a case study the Colima River in Mexico. We develop a novel point-to-point IoT measurement sounding system that does not require decoding of LoRa propriety bursts and provides accurate power versus distance profiles along the riparian zone of a steeply dropping mountain river. We used this system to obtain the measurements reported in this work, which are also analyzed and modeled. The results show that the LoRa signal propagation over water exhibits a log-normal distribution. As a result of the chirp signal processing, two new experimental path loss models are presented. The path loss results show a considerable degradation of the received signal power over water within vegetation and less signal degradation at antenna heights closer to the water surface.

Routing protocols for mobile ad hoc networks usually discover routes by flooding the entire network with control packets; this technique is known as blind flooding. This paper presents NARD, a neighbor-assisted route discovery protocol for wireless ad hoc networks. In NARD, a source node floods a limited portion of the network looking not only for the destination node, but also for routing information of other nodes (called neighbors) that were known to be near the destination node recently. Neighbor nodes can be used as anchor points where a second limited flooding takes place in search for the destination node. Because only a limited portion of the network is flooded by control packets near the source and destination nodes, NARD can significantly reduce the signaling overhead of route discovery compared with blind flooding techniques. Simulations with NS2 were undertaken to verify the validity of our approach.